Stabilized mineral oil lubricant compositions



United States Patent STABILIZED MINERAL OIL LUBRICANT COMPOSITIONS Troy L. Cantrell, Lansdowne, and Herschel G. Smith, Wallingford, Pa., assignors to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania N0 Drawing. Application June 20, 1949, Serial No. 100,308

2 Claims. (Cl. 252-515) This invention relates to stabilized mineral oil lubricant compositions, and more particularly, it relates to mineral oil lubricants which have been stabilized against oxidative deterioration. More specifically, this invention is concerned with improvements in mineral oil lubricant compositions containing addition agents of the type disclosed in the copending application of Smith, Cantrell and Peters, Serial No. 735,254, filed March 17, 1947, now U. S. Patent No. 2,511,744, and assigned to the same assignee as the present application.

Plain mineral lubricating oils often prove unsatisfactory in the lubrication of internal combustion engines of all types, particularly when severe operating conditions are encountered, because of the oxidative deterioration of the oil with the attendant deposition on the engine surfaces of varnish, gum or sludge. Furthermore, many lubricating oil compositions which may be satisfactory for the lubrication of other mechanisms have been found wholly unsuitable for use as turbine oils.

The formation of varnishes, gums and sludges on engine surfaces is generally ascribed, at least in part, to oxidation effects on mineral lubricating oils. The problem of oxidation is further aggravated in turbine oils because in normal use turbine oils become rapidly contaminated with water.

While the type of additive disclosed and claimed in copending application Serial No. 735,254 confers a remarkably etfective oxidation stability on mineral lubricating oils, the oils in use sometimes acquire a dark color, albeit their oxidation stability remains generally unimpaired. This darkening in color, although insignificant from the standpoint of oxidation stability, is important from the standpoint of the consumer, because to him, the darkening in color during use of the oil would normally be indicative of degradation, whether or not that is the fact. It would be advantageous, therefore, to provide mineral lubricating oils which remain light in color even after extended periods of use.

The principal object of this invention, then, is to provide mineral oil lubricant compositions which, in addition to being stabilized against oxidative deterioration, will not materially be darkened in color during use. Other objects will be apparent from the following detailed description.

These objects are accomplished by the present invention which resides in the provision of a mineral lubricating oil containing (1) 2,6-ditertiarybutyl-4-rnethyl phenol and (2) a non-resinous condensation product of from 1 to 4 mols of a xylidine, l to 4 mols of N-dimethylaniline and 0.5 to 4 mols of formaldehyde per mol of the xylidine, the condensation having been carried out in the presence of an activated clay catalyst at a temperature not in excess of 350 F. to condense together the three reactants.

We have found that when a mineral lubricating oil is stabilized against oxidative deterioration by the use of both of the additives set forth herein, darkening of the mineral lubricating oil in use is materially retarded. We have also found that the two additives unexpectedly synergize each other; that is, the antioxidant life of a mineral oil containing both additives is greater than the sum of the antioxidant effects obtained from the use of the individual additives alone.

As disclosed in U. S. Patent No. 2,265,582, 2,6-ditertiarybutyl-4-methyl phenol is by itself a good antioxidant. As disclosed in copending application Serial No. 735,254, condensation product prepared in the presence of an activated clay is in itself an excellent antioxidant, it being generally more potent than 2,6-ditertiary-butyl-4-methyl phenol, particularly under service conditions involving high temperatures. Our invention resides in using both of these antioxidants in one mineral lubricating oil to obtain as new and unexpected results the stabilization of the color of the oil during use and a synergistic elfect on the oxidation stability of the oil.

As disclosed in copending application Serial No. 735,254, the non-resinous xylidine-dimethylaniline-formaldehyde condensation product is prepared by heating the reactants in the presence of an activated clay catalystat a temperature not in excess of 350 F. to condense together the three reactants. We have found that if the temperature of 350 F. is exceeded to any substantial extent, the condensation product formed tends to be resinous and insoluble. The preferred temperature for the condensation ranges from to 300 F. The proportions of the reactants used to prepare the condensation product vary over a relatively wide range. The xylidine is employed in an amount of from 1 to 4 mols; N-dimethylaniline is employed in an amount of from 1 to 4 mols; and the amount of formaldehyde ranges from 0.5 to 4 mols of formaldehyde per mol of the xylidine. Ordinarily, it is preferred to use from 5 to 10 per cent by weight of an activated clay catalyst based on the total weight of the reactants. However, smaller amounts, as low as l per cent by weight, and larger amounts, as high as 20 per cent by weight, can be used; but larger amounts than about 10 per cent by weight are ordinarily not necessary. Contrary to what may be expected from the nature of the reactants, highly condensed insoluble resinous products are not obtained. On the contrary, when the above reactants are condensed in accordance with the copending application above referred to, there are obtained light-colored condensation products which arle non-resinous and which are readily soluble in mineral 01 S.

Any of the six isomeric xylidines or mixtures thereof are used in the preparation of the condensation products; 2,4-xylidine is preferred.

In lieu of formaldehyde in the condensation reaction, any formaldehyde-yielding compound can be used, such as paraformaldehyde, dioxymethylene and trioxymethylene. In such case, the amount of formaldehyde-yielding compound used is based on the equivalent number of mols of formaldehyde yielded within the range of proportions of formaldehyde set forth hereinabove. Accordingly, as used in the appended claims, the term formaldehyde is intended to include formaldehyde-yielding compounds as well as formaldehyde itself.

Various activated clay catalysts are employed in the preparation of the xylidine-dimethylaniline-formaldehyde condensation product. Such materials are well known in the art and comprise a natural clay, such as bentonite, fullers earth, floridin and smectite, which has been acid treated in order to activate the clay. These materials are described in U. S. Patent No. 1,898,165, for example.

In preparing the xylidine-dimethylaniline-formaldehyde condensation product, the reactants and catalyst are placed in a reaction vessel which is then closed and the mixture heated with agitation until all of the formaldehyde or formaldehyde-yielding compound has been consumed. At this time the water which is formed as a result of the condensation is removed, preferably under vacuum, and the dehydrated condensation product is then filtered to remove the activated clay catalyst. If it is desired, the condensation product may be prepared in a concentrate in a mineral lubricating oil which may then be diluted with additional oil to the final concentration desired. These condensation products are liquids or crystalline solids and contain in combination all three of the reactants employed in their preparation. As shown in the copending application hereinabove referred to, the use of an activated clay as a catalyst is essential in the preparation of the condensation products; otherwise black, insoluble, resinous condensation products are ob tained.

The other agent, 2,6-ditertiarybutyl-4-methyl phenol, which we employ in the lubricants of this invention, may the non-resinous xylidine-dimethylaniline-formaldehyde be obtained from any suitable source. One method of preparing 2,6-ditertiarybutyl-4-n1ethyl phenol is disclosed in U. S. Patent No. 2,265,582 and comprises alkylating para cresol with isobutylene until no more isobutylene reacts with the para cresol.

For the purposes of the present invention, the xylidinedimethylaniline-formaldehyde condensation product and 2,6-ditertiarylbuty1-4-methyl phenol are added to mineral lubricating oils in minor amounts, say in a total amount of both additives of from 0.01 to 1.0 per cent by weight on the mineral oil, sufficient to inhibit oxidative deterioration of the oil. Larger amounts of our additives may be used if desired, but it is ordinarily unnecessary to do so. Within the total amounts of both additives set forth herein, each additive may range from 20 to 80 per cent by weight of the total, i. e., in a weight ratio of from 1:4 to 4:1. Stated in another way, in order to obtain the desired results as to retardation of darkening in color, at least 20 per cent by weight of the total additives should be 2,6-ditertiarylbutyl-4-methy1 phenol; and in order to obtain the beneficial effects of the condensation product in prolonging oxidation stability, at least 20 per cent by weight of the total additives should be the xylidine-dimethyl-aniline-formaldehyde condensation product. The synergistic effects of the additives on each other with respect to antioxidant potency are also limited by the foregoing, but are obtained over the whole range of proportions of total additive disclosed herein.

The following examples are illustrative of our invention. The oxidation test referred to therein is a standard test designated ASTM D 943-47 T. Briefly, the test comprises subjecting the oil sample to oxygen at a temperature of 95 C. (203 F.) in the presence of water and an iron-copper catalyst, and determining the time required to build up a neutralization number of 2.0. The flow of oxygen is maintained at 3 liters per hour. The remarkably effective stability to oxidation of the mineral oil lubricant compositions containing our new addition agents, the color improvements and the synergistic effects are illustrated by the results shown in the following examples:

Example I.--A portion of turbine oil stock Was treated with 0.2 per cent by weight of (A) 2,6-ditertiarybutyl-4- methyl phenol, and another portion of this stock was treated with 0.2 per cent by weight of (B) the condensation product of 1 mol of 2,4-xylidine, 1 mol of N-dimethylaniline and 1 mol of formaldehyde, prepared in the presence of 10 per cent by weight of Filtrol (activated clay) as set forth in the above-identified copending application. A third portion was treated with both 0.2 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.2 per cent by weight of (B) the condensation product of 2,4-xylidine, N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) exhibited the following properties:

Base Oil gas? gas? Oil Conaz'nylon a on ainmg Base ing 0.2% ing 0.2% of (A) and of (A) of (B; 0.2% of Gravity, API 28. 28. 4 28. 4 28. 3 Viscosity, SUV, 100 F- 610 611 010 611 Flash, 00, F 490 490 490 490 Pour, F +5 +5 +5 +5 Color, NPA 2. 5 2. 5 2. 5 2. 5 Oxidation Test, ASTM Time oxidized, hrs... 219 400 1, 600 2, 650 Neutralization No. 2. 0 2.0 2.0 2. 0 Expected time oxidized, hrs 2, 000 Increase over expected time oxidized, hrs 650 Color of oxidized oil after 14 days oxidation test, NPA.- 5.0 2 5 4. 5 2. 5

Example II.A portion of turbine oil stock was treated with 0.1 per cent by weight of (A) 2,6-ditertiarybutyl- 4-methyl phenol, and another portion of this stock was treated with 0.1 per cent by weight of (B) the condensation product of 1 mol of 2,4-xylidine, 4 mols of N-dimethylaniline and 4 mols of formaldehyde, prepared as de scribed in the above-identified copending application. A third portion was treated with both 0.1 per cent by weight of (A) 2,6-ditertiarylbutyl-4-methyl phenol and 0.1 per cent by weight of (B) the condensation product of 2,4- xylidine, N-dimethylaniline and formaldehyde. The base 4 with (A), the oil blended with (B). with both (A) and (B) showed the oil, the oil blended and the oil blended following results:

Example III.-A portion of turbine oil stock was treated with 0.4 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol, and another portion of this stock was treated with 0.4 per cent by weight of (B) the cond-ensation product of 2 mols of 2,4-xylidine, 1 mol of N- dimethylaniline and 2 mols of formaldehyde prepared as described in the above-identified copending application. A third portion was treated with both 0.4 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.4 per cent by weight of (B) the condensation product of xylidine, N-dimethyl-aniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) showed the following results:

Base Oil East; Oil gas? Oil 1(ilontaii ryion ainon aing 0. 0

Base ing 0.4% ing 0.4% of (A) and of (A) of (B, 0.4%

Oxidation test, ASTM Time oxidized, hrs... 195 1, 400 4, 6, 200

Neutralization N o. 2.0 2.0 2.0 2.0 Expected time oxidized, hrs 5, 500 Increase over expected time oxidized, hrs 700 Color of oil after 14 days oxidation test, NPA 5.0 2.0 5. 0 2.0

Example IV.A portlon of turbine 011 stock was treated with 0.08 per cent by weight of (A) 2,6-d1tertiarybutyl-4-methyl phenol, and another portion of this stock was treated with 0.32 per cent by weight of (B) the condensation product of 2 mols of meta xylidine, 1 mol of N-dimethylaniline and 2 mols of formaldehyde prepared as described in the above identified copending application. A third portion was treated with both 0.08 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol and 0.32 per cent by weight of (B) the condensation product of xylidine, N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) showed the following results:

Example V.A portion of turbine oil stock was treated with 0.32 per cent by weight of (A) 2,6-ditertiarybutyl-4-methyl phenol and another portion of this stock was treated with 0.08 per cent by weight of (B), the condensation product of 2 mols of meta xylidine, 1 mol of N-dimethylaniline and 2 mols of formaldehyde, prepared as described in the above-identified copending application. A third portion of the turbine oil stock was treated with both 0.32 per cent by weight of (A) 2,6-ditertiarybutyl-4-rnethyl phenol and 0.08 per cent by weight of (B) the condensation product of xylidine, N-dimethylaniline and formaldehyde. The base oil, the oil blended with (A), the oil blended with (B), and the oil blended with both (A) and (B) showed the following properties:

Base Oil (East; Oil (East: Oil Colattgig; on ainon aining a Base 011 ing 0.32% ing 0.08% of (A) and of (A) of (B) 0.08% of Oxidation Test, AS'IM Time oxidized, hrs... 195 1, 085 350 l, 700 Neutralization No 2.0 2.0 2.0 2. Expected time oxidized, hrs 1, 435 Increase over expected time oxidized, hrs 265 Color of oil after 14 days oxidation st, N 5.0 2.0 5.0 2. 0

The preceding examples clearly illustrate the remarkable properties of our new mineral oil lubricant compositions. The color tests made during oxidation show that the base oil and the oil containing the xylidine-dimethylaniline formaldehyde condensation product alone turned dark during oxidation, while the oil containing both additives in accordance with the present invention retained its pristine color. The color test referred to is described in ASTM Standards on Petroleum Products and Lubricants, November 1948, pages 105-109 (ASTM D 15545 T). A National Petroleum Association (NPA) color number of 2 designates an oil slightly darker than cream white, namely extra pale. Also significant is the fact that while the lubricating oil containing the xylidine-dimethylaniline-formaldehyde condensation products alone turned dark during oxidation, only a small amount of 2,6-ditertiarybutyl-4-methyl .phenol need be added to give an NPA color of 2. Thus,

a base oil containing 0.32 per cent by weight on the oil of the condensation product of xylidine, N-dimethylaniline and formaldehyde will turn dark during oxidation; but if only 0.08 per cent by weight on the oil of 2,6-ditertiarybutyl-4-methyl phenol is added, the oil will not turn dark.

In addition to color improvement, the above examples clearly show the unexpected synergistic effect with respect to antioxidant potency obtained in accordance with the present invention. In preceding Example I, for instance, the lubricating oil containing the combination of mgredients was much more stable to oxidation than oils containing the ingredients separately. The oil containing only 2,6-ditertiarybutyl-4-methyl phenol had an antioxidant life of 400 hours. The oil containing only the xylidine dimethylaniline formaldehyde condensation product had an antioxidant life of 1600 hours. It would be expected, therefore, that an oil containing both ingredients would have an antioxidant life of about 2000 hours. However, the test shows that the improved oil of this invention had an antioxidant life of 2650 hours, indicating an unexpected synergistic efiect.

The above examples also show the remarkable oxidation stability imparted to mineral oil lubricant compositions by the use of our new addition agents. Mineral oil lubricant compositions containing our new addition agents are therefore eminently suited for use where the operating conditions are extremely severe, as in diesel, tank and truck engines, and in the lubrication of steam turbines. Furthermore, the beneficial effects of our invention may be applied to all types of lubricating oil basekstocks, that is, paraifinic, naphthenic and mixed base stoc s.

If desired, other known addition agents may be incorporated into the lubricant composition prepared in accordance with our invention. For example, pour point depressants, extreme-pressure agents, and the like may be added. Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

We claim:

1. A lubricant composition comprising a major amount of a mineral lubricating oil and minor amounts in a total of from 0.01 to 1 per cent by weight of said oil, of: (1) 2,6-ditertiarybutyl-4-methyl phenol; and (2) a non-resinous condensation product of 1 mol of a xylidine, 1 mol of N-dimethylaniline and 1 mol of formaldehyde, the condensation of said product having been carried out in the presence of an activated clay catalyst at a tempera ture not in excess of 350 F. to condense together the three reactants; the amounts of (1) and (2) with respect to each other being in a weight ratio ranging from 1:4 to 4'1 The composition of claim 1, wherein each of the compounds (1) and (2) is present in an amount of 0.2 per cent by weight.

References Cited in the file of this patent UNITED STATES PATENTS 2,202,825 Brandes June 4, 1940 2,225,533 Dewey Dec. 17, 1940 2,375,168 Hardman May 1, 1945 2,410,652 Griflin Nov. 5, 1946 2,440,530 Yates Apr. 27, 1948 2,511,744 Smith et a1. June 13, 1950 OTHER REFERENCES Motor Oils and Engine Lubrication, Georgi, Reinhold Pub. C0., 1950; pages 27 and 28 pertinent.

Lubricating Oil Additives, part IV, by Kalichevsky, in Petroleum Refiner of Sept. 1949, vol. 28, No. 9; pages and 86 pertinent. 

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A MINERAL LUBRICATING OIL AND MINOR AMOUNTS IN A TOTAL OF FROM 0.01 TO 1 PER CENT BY WEIGHT OF SAID OIL, OF: (1) 2,6-DITERTIARYBUTYL-4-METHYL PHENOL; AND (2) A NON-RESINOUS CONDENSATION PRODUCT OF 1 MOL OF A XYLIDINE, 1 MOL OF N-DIMETHYLANILINE AND 1 MOL OF FORMALDEHYDE, THE CONDENSATION OF SAID PRODUCT HAVING BEEN CARRIED OUT IN THE PRESENCE OF AN ACTIVATED CLAY CATALYST AT A TEMPERATURE NOT IN EXCESS OF 350* F. TO CONDENSE TOGETHER THE THREE RECTANTS; THE AMOUNTS OF (1) AND (2) WITH RESPECT TO EACH OTHER BEING IN A WEIGHT RATIO RANGING FROM 1:4 TO 4:1. 